I have calculated the phonon dispersion of orthorhombic RbPbI3 (Pnma) using "PHONON" as implemented in Quantum Espresso and found the negative frequencies ( which should not be present as suggested in https://doi.org/10.1063/1.5131575). It would be great help if you suggest to me where I am doing wrong!!! I have provided the computational details below: 1) The structure first is being relaxed and then the convergence tests are performed for Ecut, Kmesh and Lattice parameters. 2) Using the relaxed structure with converged parameters, SCF is performed with cov_thr=1.0d-8 (ecutwfc=70, ecutrho=600, kmesh=12*6*3); phonon calculation is performed with tr2_ph=1.0d-14 at Gamma point, frequencies are obtained by imposing acoustic sum rule at the Gamma point with asr=simple.
Thank you!! -- With regards Anupriya Nyayban Ph.D. Scholar Department of Physics NIT Silchar
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